The evolution of so-called 4G wireless communications networks such as Long Term Evolution (LTE) and LTE-Advanced (LTE-A), is being driving by customer demand for higher capacity and peak throughput. A number of approaches have been developed to meet such demand. However, low data rate cell-edge users continue to pose challenges to meeting these demands. Such users tend to be interference limited. As well, where such users are located indoors, there may be coverage gaps that constrain performance.
Coordinated Multi-Point (CoMP) is a framework of methods to improve both peak user throughput as well as aggregated network throughput in a mobile cellular network. These methods employ multiple access points or base stations (in the LTE environment, known as evolved Node Bs or eNodeBs or eNBs) grouped in a CoMP set of cooperating nodes to communicate with a wireless device (a User Equipment in LTE) of interest. Examples of CoMP methods are disclosed in Dahlmann, Erik et al., “3G Evolution: HSPA and LTE for Mobile Broadband”, Academic Press, 2007, which is incorporated by reference in its entirety herein.
CoMP methods may be configured in either a centralized coordinated approach or through a distributed processing architecture to improve capacity. A centralized approach to CoMP where a central node or server coordinates CoMP transmissions between in CoMP set benefits from complete knowledge of the CoMP signals and context. However, such approaches rely on high capacity backhaul interconnects (e.g, via an X2 interface) between the base stations in the CoMP set. Centralized CoMP transmission and reception techniques use multiple transmit and receive antennas from different locations, to send/receive data and to reduce signal interference to the UE. In contrast, distributed processing architectures for CoMP may achieve lower latency and reduced backhaul complexity but may experience reduced performance relative to a centralized CoMP approach.
In LTE-A, CoMP currently includes methods such as Coordinated Scheduling (CS), Coordinated Beamforming (CB), Joint Processing (JP) and Dynamic Point Selection (DPS).
In CS, the resource assignment is coordinated among multiple base stations, and transmitted/received from/to a selected base station. In CB, coordination among base stations or access points is coordinated so that their transmissions are beamformed and directed toward the UE. In downlink (DL) JP, common data is transmitted by multiple base stations and processed jointly by the UE. In uplink (UL) JP, data from the UE is provided to multiple base stations. Two challenges faced in JP, especially UL JP, are the backhaul latency and the backhaul bandwidth called for to transmit data from the receiving base stations to a single process node, which may, in some implementations, be a base station.
Existing CoMP implementations may require extremely high levels of backhaul latency to exchange all of the available data between base stations, especially in JP. For example, during upload of large data files using JP, all of the received UL data will be transferred from one or more CoMP cooperating eNBs to the CoMP serving eNB requiring a high capacity over the X2 interfaces extending between the eNBs. The capacity called for may be on the order of 10s or 100s of Gbps. This can impose a significant cost constraint to the implementation of UL JP. Furthermore, the exchange of large amounts of data over the X2 interfaces between cooperating eNBs may result in significant latency.